Document DE 199 60 621 B4 describes a hybrid drive of this type having three embodiments of a manual transmission. In all variants, the power transmission branch of the manual transmission associated with the internal combustion engine comprises a first countershaft, which can be brought into a drive connection to the drive shaft of an internal combustion engine on the input side by means of an input constant, a first input shaft, and a friction coupling, and which can be brought into a drive connection to an output shaft on the output side by means of a first group of selectively shiftable gearwheel sets. In the first variant embodiment according to FIG. 1 therein, a second input shaft is designed as a second countershaft, which is connected in a rotationally fixed manner to the rotor of an electric machine and can be brought into a drive connection to the output shaft by means of a second group of selectively shiftable gearwheel sets. In this case, the initially mentioned coupling-shift element is designed as a shifting clutch, which is disposed between the drive wheel—on the countershaft side—of a drive stage disposed between the first input shaft and the second input shaft, and the second countershaft.
In the second and third embodiments according to FIGS. 2 and 3 therein, the second input shaft is designed as a hollow rotor shaft, which is coaxially disposed over the first input shaft and is connected in a rotationally fixed manner to the rotor of an electric machine, which is coaxially disposed over the first input shaft. The rotor shaft is connected in a driving manner by means of a second input constant to the second countershaft, which can be brought into a drive connection to the output shaft by means of the second group of selectively shiftable gearwheel sets. In this case, the coupling-shift element is designed as a shifting clutch, which is disposed between the first input shaft and the rotor shaft.
In another hybrid drive of this type, according to WO 2008/138 387 A1, the two input shafts of the applicable manual transmission are designed as countershafts. The first input shaft or countershaft of the power transmission branch associated with the internal combustion engine can be connected to the drive shaft of an internal combustion engine on the input side by means of a controllable separating clutch, and can be brought into a drive connection to an output shaft on the output side by means of a first group of selectively shiftable gearwheel sets. The second input shaft or countershaft of the power transmission branch associated with the electric motor is connected in a rotationally fixed manner to the rotor of an electric machine on the input side, and can be brought into a drive connection to the output shaft on the output side by means of a second group of selectively shiftable gearwheel sets. The gearwheel sets of both groups are disposed in common radial planes and each use a common output gear disposed on the output shaft. The idler gears and the associated gear clutches of two axially adjacent gearwheel sets of the second group are combined in a shifting group and are disposed on the output shaft. As a result, the gear clutches of the gearwheel sets of the first group that use the same idler gears also function as coupling-shift elements, by means of which both input shafts can be coupled independently of the shifting of one of the applicable gearwheel sets.
Document DE 10 2010 030 569 A1, which was not previously published, makes known various embodiments of a hybrid drive of the type in question, in which the applicable manual transmission is derived from a double clutch transmission having two coaxially disposed input shafts. While the centrally disposed, first input shaft can be connected to the drive shaft of the internal combustion engine by means of a separating clutch, the second input shaft, which is designed as a hollow shaft and is coaxially disposed over the first input shaft, has a drive connection to the rotor of the electric machine directly or by means of an input transmission stage. The coupling-shift element for coupling the two input shafts is designed as a friction clutch or a claw clutch, and is disposed external to the transmission directly between the two input shafts.
The hybrid drive under consideration here can therefore be implemented with manual transmissions having different designs. However, a common feature of all embodiments of manual transmissions is that each one comprises a power transmission branch associated with the internal combustion engine and a power transmission branch associated with the electric motor, which are combined at the output shaft. In each case, the power transmission branch associated with the internal combustion engine comprises the first input shaft, the gearwheel sets of the first group, and the output shaft, and enables torque to be transferred between the internal combustion engine and the drive wheels of the motor vehicle, which have a drive connection to the output shaft. In each case, the power transmission branch associated with the electric motor comprises the second input shaft, the gearwheel sets of the second group, and the output shaft, and enables torque to be transferred between the electric motor and the drive wheels of the motor vehicle.
In this type of hybrid drive, with the coupling-shift element disengaged, a drive operation using only the internal combustion engine can therefore be implemented by engaging a gearwheel set of the first group, a drive operation using only an electric motor can be implemented by engaging a gearwheel set of the second group, and a combination drive operation of both assemblies (internal combustion engine and electric machine) with the electric machine in a motor mode or a generator mode can be implemented by engaging a gearwheel set of both the first and second groups.
Gear shifts can also be implemented as power shifts within one group of gearwheel sets by at least partially maintaining the tractive force during the gear shift by means of the assembly (internal combustion engine or electric machine) assigned to the other group of gearwheel sets, by means of a gearwheel set engaged therein.
The internal combustion engine can be started using the electric machine by engaging the coupling-shift element with the motor vehicle at a standstill. Engaging the coupling-shift element also makes the gearwheel sets of the second group available for the drive operation using the internal combustion engine, and makes the gearwheel sets of the first group available for the drive operation using the electric motor. Therefore, given an appropriate gear ratio and assignment of the gearwheel sets, fewer gearwheel sets are required overall and the manual transmission can therefore have a simpler and more compact design.
The disadvantage of these known hybrid drives is that a gear shift implemented in the manual transmission during an electric drive operation, i.e. with the internal combustion engine shut off and/or decoupled by disengaging the separating clutch, is necessarily associated with an interruption of tractive force, which results in unwanted losses of comfort and dynamics. In addition, the gear clutches of the gearwheel sets of the first group cannot be externally synchronized during an electric drive operation and must therefore be designed as synchronous clutches.